Summary: mARUS37, 207--213 (1979)
Ammonia Photolysisand the Greenhouse Effect in the
Primordial Atmosphere of the Earth
W. R. KUHN AND S. K. ATREYA
Department of Atmospheric and OceanicScience, Space Physics ResearchLaboratory,
The University of Michigan, Ann Arbor, Michigan 48109
Received March 28, 1978; revised July 5, 1978
Photochemical calculations indicate that in the prebiotic atmosphere of the Earth am-
monia would have been irreversibly converted to N2 in less than 40 years if the ammonia
surface mixing ratio were _~10-4. However, if a continuous outgassing of ammonia were
maintained, radiative equilibrium calculations indicate that a surface mixing ratio of am-
monia of 10-5 or greater would provide a sufficient greenhouse effect to keep the surface
temperature above freezing. With a 10-4 mixing ratio of ammonia, 60 to 70cfvof the present
day solar luminosity would be adequate to maintain surface temperatures above freezing.
A lower limit to the time constant for accumulation of an amount of nitrogen equivalent
to the present day value is 10 my if the outgassing were such as to provide a continuous
surface mixing ratio of ammonia ~ 10-5.
INTRODUCTION
The importance of NH3 to the primitive
atmosphere, if indeed it was present, is